Hard precious material

ABSTRACT

A hard precious material having the appearance of a precious metal such as gold, platinum or silver, wherein a precious metal such as gold, platinum or silver is finely distributed in a base of ceramic material having a high hardness exceeding 6 Mohs, the fritted body of these constituents being polished to give the appearance of a precious metal.

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States atet Revaz Aug. 26, 1975 [54] HARD PRECIOUS MATERIAL 2,414,368 1/1947 Feichtfil' 106/42 x 2,488,507 11 1949 Burdick 63/32 [75] Invent Frncls Rev, Le Lode 2,631,106 3/1953 Mitkewich. l06/42 swltlerland 2,690,630 10 1954 Eversole 63 32 2,723,915 11 1955 Merker 106 42 [73] Assgnee i P 's? 3,442,666 5/1969 Berghezanm. 106/42 x 6 3,489,627 1 1970 Botden et al. 106/42 x [22] Filed; Dec 5 1972 3,528,847 9/1970 Grego et al. 106/73.4 X

App]. No.: 312,346

Foreign Application Priority Data Dec. 10, 1971 Switzerland 18015/71 U.S. c1. 106/42; 106/65; l06/73.4;

63/32 161. c1. 00413 35/00 Field 61 Search 106/42, 65, 73.4; 63/32 References Cited UNITED STATES PATENTS 12/1925 Bertolini 106/42 X 5/1942 Weiss 63/32 Primary Examiner-Winston A. Douglas Assistant ExaminerJohn F. Niebling Attorney, Agent, or Firmlmirie, Smiley & Linn [5 7 ABSTRACT 6 Claims, N0 Drawings HARD RRECHOUS MATERIAL BACKGROUND OF THE INVENTION This invention relates to a hard precious material having the appearance of a precious metal such as gold, platinum or silver, a method for producing this hard precious material and the use of the same.

Jewelry made of precious metals such as gold, platinum and silver and their alloys are scratched when such jewelry is bumped against or slid over hard objects. This is easily understood when considering that the Mohs hardness of gold and its usual alloys is in the order of 2 to 3. Any object having a hardness exceeding a value of 3 in the scale of Mohs will scratch jewelry made of gold. Practically a high number of materials have a hardness exceeding a value of 3 in the scale of Mohs, for instance glass, bricks, cement and concrete. It would thus be desirable that jewelry worn in normal daily life having hardness in the order of 8 or 9 Mohs in order to conserve its original brilliancy and appearance of a precious metal.

SUMMARY OF THE INVENTION It is an object of this invention to obtain a material having the advantages of a hard material together with the appearance and the brilliancy of precious metals such as gold, and possibly silver, platinum and others.

In accordance with this invention such a material is obtained by distribution of a precious metal within a matrix or base of ceramic material having a hardness exceeding 6 Mohs, the precious metal occupying 7.5 to 70% of the volume of a body made of the material.

This invention also relates to a method for producing a hard precious material as defined above, this method broadly comprising thoroughly mixing 30 to 92.5 volume-% of ceramic material having a Mohs hardness exceeding 6 with 7.5 to 70 volume-% of a precious metal, adding to this mixture a small percentage of mineral oxides for assisting sintering and of organic binding agents for facilitating pressing, the mixture in powder form is pressed into the desired shape, the dimensions of this shape exceeding the nominal final dimensions for compensating shrinkage during the following sintering operation, the objects obtained in this way are heated to 100 to 200 C for eliminating said organic binding agents, and then sintering at temperatures ex- .ceeding 1400 C is effected, whereafter the objects are polished in order to obtain the required brilliancy for use.

The degree of shrinkage varies considerably. It depends particularly on the percentage of precious metal used, but also on the type of the ceramic base or matrix material used. The degree of shrinkage may vary from 5 to 25%. Usually it has to be determined by experiment for any type of composition of the material and manufacturing method, in that samples of the material are made and the degree of shrinkage is measured.

The hard precious material obtained by this method is preferably used for making jewelry. All kindsofjewelry may be made such as rings, chains, bracelets, brooches, long neck chains and bracelets for wrist watches. The material may also be used as a sliding body or bearing portion, the precious metal imparting to the composed material its low friction coefficient and the ceramic matrix or base imparting to the material its high resistance to wear. The material may particularly well be used for making watch cases.

This invention will now be described first in its general aspect and then by means of a number of specific examples of the method for producing the hard precious material.

DETAILED DESCRIPTION OF THE INVENTION First 30 92.5 volume-% of very pure alumina powder are thoroughly mixed with to 7.5 volume-% of gold. A small percentage of mineral oxides for assisting sintering and of organic binding agents for facilitating pressing and shaping of the mixture are then added to the same. Afterwards this mixture is pressed in a form for obtaining the desired shape, whereby the size or dimensions are selected such that after shrinkage of the object during sintering the required final shape and dimensions are obtained. The shaped objects are then heated to to 200 C for eliminating the organic binding agents, whereafter the objects are sintered at 1400 to 1600 C. The gold which is in liquid state at these sintering temperatures remains uniformly distributed in the skeleton of the ceramic material by capillarity. After sintering, the objects are polished in order to obtain the necessary brilliancy for their use in jewelry. In this manner the gold is uniformly distributed in a skeleton of hard ceramic material, namely in corundum when alumina powder is used as a base material as set out above.

More specific examples will now be given for obtaining hard precious materials in accordance with this invention: I

EXAMPLE 1 7.7 volume-% of gold powder are thoroughly mixed with 92.3 volume% of highly pure alumina powder. 1 volume-% of MgO and Ga O is added to this mixture for assisting compaction during sintering. An organic binding agent, for instance 1 weight-% of polyvinyl alcohol or 0.5 weigth-% of stearic acid are further added for facilitating pressing of the mixture. The mixture is now pressed into the desired shape and size, taking care of selecting the dimensions such that after shinkage of the formed object during sintering the required dimensions are obtained. The objects are now heated to 100 to 200 C for eliminating the organic binding agents. The objects are then sintered at 1600 C, whereafter they are polished as explained above. The hardness is of 1250 to 16S0 Knoop this corresponding to 7 to 8 in the scale of Mohs. The degree of shrinkage to be taken into consideration is in the order of 14%.

EXAMPLE 2 14.2 volume-% of gold is thoroughly mixed with 85.8 volume-% of highly pure powder of alumina. The mineral oxides and binding agents of example 1 are added. The mixture is pressed and the objects thus obtained are calcined at a termperature between 100 and 200 C for eliminating the organic binding agents. The objects are then sintered at 1650 C. The Knoop hardness is comprised between 1250 and 1450, this corresponding to a hardness of Mohs of 7 to 7.5. The shrinkage to be considered is in the order of 13%.

EXAMPLE 3 25,0 volume-% of gold are mixed with 75.0 volumeof highly pure alumina powder. The method then proceeds according to example 1. The sintering temperature is 1650 C. The Knoop hardness is between 1150' and 1250, this corresponding to a Mohs hardness of 7. The shrinkage is in the order of 10%.

EXAMPLE 4 35.0 volume-% of gold are carefully mixed with 65.0 volume-% of highly pure alumina powder. The method is then carried out according to example 1. Sintering is effected at 1650 C. The Knoop hardness is 920, this corresponding to a Mohs hardness of 6.5. The shrinkage is about 8%.

EXAMPLE 15.0 volume-% of gold are carefully mixed with 85.0 volume-% of a mixture composed of one mole of NiO and one mole of Ta O The same organic binding agents are added as in example 1. The objects are pressed and shaped as set out in example 1 and they are then calcined at a temperature between 100 and 200 C for eliminating the organic binding agents. The objects are then sintered at 1450 C. The Knoop hardness is of 890, this corresponding to a Mobs-hardness of 6.5. A shrinkage of about 15% has to be taken into consideration.

This example is of particular interest because the tritutile (NiO Ta O has a yellow color. It thus assists and reinforces the yellow gold color of the hard precious material obtained.

Other ceramic materials having suitable hardness may be used, such as for instance BeO (9 Mohs), ZrO with 10% of CaO or of Y O (6.5 to 8 Mohs) or spine] (MgOAl O 8 Mohs). It is also possible to use further ceramic materials such as particularly ceramic glasses (Pyroceram).

The novel material according to this invention may easily be polished by means of diamond paste similar to the paste used in lapidary mills. In view of its relatively high percentage of precious metal, this percentage being of 28 weight-% in the case of 7.5 volume-% and of 80 weight-% in the case of 45 volume-%, the material may be considered as being a precious material. The gold may be recovered by solving it by means of potassium cyanide (KCN). Platinum may be recovered by chemical solution or by melting. Silver may also be recovered by melting.

What I claim is:

1. An article of jewelry comprising a hard precious material having a hardness exceeding 6 Mohs, said material comprising a precious metal selected from the group consisting of gold, platinum and silver distrib-,

uted in a ceramic matrix of alumina, said metal occupying 7.7 to by volume of said matrix.

2. A precious material according to claim 1, wherein said matrix of ceramic material has a yellow color.

3. A precious material according to claim 1, wherein said precious metal is gold.

4. A precious material according to claim 1, wherein said precious metal is platinum.

5. A precious material according to claim 1, wherein said precious metal is silver.

6. An article of jewelry of claim 1, wherein said article is a watch case. 

1. AN ARTICLE OF JEWELRY COMPRISING A HARD PRECIOUS MATERIAL HAVING A HARDNESS EXCEEDING 6 MOHS, SAID MATERIAL COMPRISING A PRECIOUS METAL SELECTED FROM THE GROUP CONSISTING OF GOLD, PLATIUM AND SILVER DISTRIBUTED IN A CERAMIC MATRIX OF ALUMINA, SAID METAL OCCUPYING 7.7 TO 70% BY VOLUME OF SAID MATRIX.
 2. A precious material according to claim 1, wherein said matrix of ceramic material has a yellow color.
 3. A precious material according to claim 1, wherein said precious metal is gold.
 4. A precious material according to claim 1, wherein said precious metal is platinum.
 5. A precious material according to claim 1, wherein said precious metal is silver.
 6. An article of jewelry of claim 1, wherein said article is a watch case. 